|By Alwyn Scott and Daniel Trotta

|By Alwyn Scott and Daniel Trotta

NEW YORK (Reuters) - Gresham, Smith and Partners recently designed a screening area at Norfolk International Airport in Virginia with one major concern in mind: flexibility, so it can adapt to changing security threats.

From box-cutters to explosives to automatic weapons, the dangers for airport security evolve. So the firm created a large, open space without support columns that can be easily reconfigured to bring in the next generation of screening machines.

"We don't know what's coming next so we design for that," said Wilson Rayfield, executive vice president in charge of aviation at the architecture, design and consulting firm.

In the face of airport threats such as Tuesday's deadly attack in Istanbul, designers are asked to come to the frontline of the security challenge and achieve the nearly impossible: improve security without slowing down travelers.

The stakes are high. In Istanbul, three suspected Islamic State suicide bombers killed 44 people and wounded 238 in a gun and bomb attack. In Brussels on March 22, two Islamic State suicide bombers detonated suitcase bombs in the airport departure hall before a third struck a metro train in the city, killing 32 people in all.

Sometimes, art and function coincide. Open spaces and high ceilings can reduce the impact of a concussive blast.

Other times, designers are working to reduce congestion in non-secure areas and create more offsite checkpoints. They seek to channel passengers in ways that take advantage of high-tech sensors, cameras and facial recognition software that may help police stop assailants before they kill.

"Aviation has a lot to learn from Las Vegas casinos," said Rayfield, referring to surveillance cameras and crowd control methods that he said allow three-fourths of visitors to be identified.

A terminal renovation soon to begin at Denver International Airport will incorporate the latest innovations, such as creating more security checkpoints dispersed throughout the airport in order to reduce crowds. At Newark Liberty International Airport, another major hub, vehicles have already been moved further from the terminal to lessen the threat of a car bomb.

In May, the U.S. Transportation Security Administration (TSA) issued a broad call for companies to devise new ways to address threats, improve passenger screening and deliver next-generation screening technology. Proposals are due later this month.

ISRAEL AT FOREFRONT

Since the attacks of September 11, 2001, security experts have revolutionized their craft, sometimes by moving screening checkpoints further away from terminals, one of many tactics employed by Israel, long seen as the vanguard nation in airport security.

Ofer Lefler, a spokesman for Israel Airports Authority, said security was "100 percent" a consideration required of architects who designed Ben Gurion Airport's main terminal, though he declined to discuss specifics.

The terminal, completed in 2004, is grand with high ceilings and an abundance of marble and Jerusalem stone. A magnificent sun roof, water fountain and atrium give way to corridors leading to the gates like spokes on a wheel.

Beyond aesthetics, the design has a function, according to one Israeli aviation security consultant who spoke to Reuters on condition of anonymity as he was unauthorized to discuss measures at Ben Gurion Airport. Wide-open sight lines give security agents a clear view so that "potential terrorists can be tracked by guards, whether in person or through the closed-circuit TV system, from the moment they are arrive."

From the parking area to the terminal, there are several access points with sliding glass doors made from a blast-proof material that would help limit casualties from shrapnel, the consultant said.

Surveillance at Ben Gurion begins well before anyone reaches the parking area or terminal. Cars are stopped at a checkpoint, watched over by heavily armed guards and cameras that read license plates. People deemed suspicious are pulled over for further questioning and possibly searches. Largely surreptitious monitoring continues all the way to the terminal.

But, experts say, such measures may be impractical at busier airports. Ben Gurion handled fewer than 16 million international passengers in 2015, compared to 75 million at London Heathrow.

In the car-crazed United States, adding vehicle checkpoints to old airports would create even greater traffic jams where congestion is already colossal.

"That stops a car or bus or a truck. But it doesn't stop people," said Matthew Horace, chief security officer at FJC Security Services in Floral Park, New York.

Technology has proven to invaluable to move people quickly through the terminal, said Stanis Smith, executive vice president and airport sector leader for Stantec <STN.TO>, a Canadian design firm that is a technical adviser to a major terminal renovation at New York's La Guardia airport.

Passengers can now move twice as fast in places employing technology such as self-service check-in and baggage tagging, automated passport readers and electronic signs that can be tailored to the any particular flight.

"Just as we saw ATMs take over in the banking sector, we're seeing the same thing in the airport world," Smith said.

This includes the use of new body scanners, carry-on baggage scanning machines, and pre-airport checks to improve the flow of people and bags.

"Aviation is going to remain a favorite target," said Thomas Sanderson, director of a Washington-based think tank at the Center for Strategic and International Studies. "If someone wants to kill people, they will find a way. They just have to be right once. We have to be right all the time."